I came across the seldom-discussed topic of perfect contrition while listening to an Audio Sancto sermon. The first link is to one of the sources used in that sermon.
It takes less than twenty minutes to read and is challenging in every best sense of the term regarding salvation and sanctity. It is deeply encouraging for anyone so unfortunate as to have fallen into mortal sin.
The second link is from the old Catholic Encyclopedia, about Johann Cardinal Franzelin, SJ, raised to high office by Bl. Pius IX, and who is mentioned in the booklet given in the above link.